<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <title>OpenLayers Grayscale OSM Example</title>
    <link rel="stylesheet" href="../theme/default/style.css" type="text/css">
    <link rel="stylesheet" href="style.css" type="text/css">
    <script src="../lib/OpenLayers.js"></script>
    <script type="text/javascript">
        var map, layer;

        function init() {
            if (!OpenLayers.CANVAS_SUPPORTED) {
                var unsupported = OpenLayers.Util.getElement('unsupported');
                unsupported.innerHTML = 'Your browser does not support canvas, nothing to see here !';
            }

            layer = new OpenLayers.Layer.OSM('Simple OSM Map', null, {
                eventListeners: {
                    tileloaded: function(evt) {
                        var ctx = evt.tile.getCanvasContext();
                        if (ctx) {
                            var imgd = ctx.getImageData(0, 0, evt.tile.size.w, evt.tile.size.h);
                            var pix = imgd.data;
                            for (var i = 0, n = pix.length; i < n; i += 4) {
                                pix[i] = pix[i + 1] = pix[i + 2] = (3 * pix[i] + 4 * pix[i + 1] + pix[i + 2]) / 8;
                            }
                            ctx.putImageData(imgd, 0, 0);
                            evt.tile.imgDiv.removeAttribute("crossorigin");
                            evt.tile.imgDiv.src = ctx.canvas.toDataURL();
                        }
                    }
                }
            });

            // If you get a security error because the tile are not
            // from the same domain as this page, a simple Apache
            // proxy can be created to workaround this issue:
            //
            // <Proxy *>
            // Order deny,allow
            // Allow from localhost
            // </Proxy>
            // ProxyPass /osm http://tile.openstreetmap.org/
            //
            // Then, in the layer definition above, replace null with '/osm/${z}/${x}/${y}.png'

            map = new OpenLayers.Map('map', {
                layers: [layer],
                zoom: 3,
                center: [-1081125, 6212801]
            });
        }
    </script>
  </head>
  <body onload="init()">
    <h1 id="title">Grayscale OSM Example</h1>

    <div id="tags">
        openstreetmap canvas grayscale light
    </div>

    <div id="shortdesc">Show an OSM Map in grayscale</div>

    <div id="map" class="smallmap"></div>

    <div id="docs">
        <p>This example shows an OSM layer where the tiles were
        converted to grayscale
        with <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html">canvas</a>.</p>
        <p style="color:red;" id="unsupported"></p>
    </div>

  </body>
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